Conventional computer systems include system memory, which is typically used to store information, such as instructions of a software application to be executed by a processor, as well as data that that is processed by the processor. In a typical computer system, the processor communicates with the system memory through a processor bus and a memory controller. The processor issues a memory request, which includes a memory command, such as a read command, and an address designating the location from which data or instructions are to be read. The memory controller uses the command and address to generate appropriate command signals as well as row and column addresses, which are applied to the system memory. In response to the commands and addresses, data are transferred between the system memory and the processor. The memory controller is often part of a system controller, which also includes bus bridge circuitry for coupling the processor bus to an expansion bus, such as a PCI bus.
Generally, the system memory of a computer system takes the form of one or more memory modules that includes several integrated circuit memory devices mounted on a printed circuit board. Examples of the types of memory devices include asynchronous dynamic random access memories (“DRAMs”) and synchronous DRAMs (“SDRAMs”). Typically, the memory modules are removably plugged into connectors located on a motherboard of the computer system. The size of the computer system's memory can be increased by plugging additional memory modules into the motherboard. Memory modules are commercially available in standardized configurations, such as a single in-line memory module (“SIMM”) and a double in-line memory module (“DIMM”), which match the connectors. The memory modules are electrically coupled to the memory controller, processor, and other devices also mounted on the mother-board using standardized memory interfaces, as well known. These standardized memory interfaces generally include a data bus, an address bus, and a control/status bus.
Often included on the printed circuit board of a memory module is a non-volatile memory in which module specific information, such as timing information, memory type, and manufacturing information, is stored. The non-volatile memory of each module can be coupled to the memory controller on the mother board through a serial bus and the connector in which the memory module is inserted. The module specific information stored in the non-volatile memory is accessed by the computer system at start-up to initialize the memory controller so that it can communicate with the memory devices of the memory module. Additionally, the basic input/output system (BIOS) or operating system of the computer system may further access the module specific information through the serial bus in performing various tasks.
A memory system that has been developed as an approach to increasing system memory bandwidth employs multiple memory devices coupled to the processor through a “memory hub.” In a memory hub architecture, or a hub-based memory sub-system, a system controller or memory controller is coupled over a high speed data link to several memory modules. Typically, the memory modules are coupled in a point-to-point or daisy chain architecture such that the memory modules are connected one to another in series. Each memory module includes a memory hub that is coupled to the corresponding high speed data links and a number of memory devices on the module, with the memory hubs efficiently routing memory requests and responses between the controller and the memory devices over the high speed data links.
A non-volatile memory is still included on the memory module for providing module specific information to the system controller of the host computer system, in the same manner as the memory module for the standard system memory configuration previously discussed. That is, the system controller is coupled through a serial bus and module connector to the non-volatile memory in order to read the module specific information as part of initializing the computer system. With the addition of a memory hub to the memory module, a printed circuit board having more space is required. However, in some applications, such as in hand-held computing devices or portable computers, space allocated to memory modules is at a premium, and consequently, increasing the size of the printed circuit board to accommodate the additional components is undesirable. Additionally, the time for completing initialization of the computer system upon power up will be limited by the speed at which the non-volatile memory of each of the memory modules in a system memory can be accessed and the information transferred to the system controller over the serial bus. In applications where the demand for processing capability is immediate, minimizing the time for initializing the computer system is desirable.